In recent years, hybrid cars have been developed also in the field of construction equipment, just like in the field of ordinary automobiles. The hybrid construction equipment of this type is provided with an engine, a motor-generator, an electrical storage device, and a working machine. Here, the electrical storage device is a battery capable of charging and discharging freely, and is constituted by a capacitor or a secondary battery. It should be noted that the present invention will be explained using a capacitor as a representative of the electrical storage devices hereinafter. A capacitor as the electrical storage device stores electric power which is generated when the motor-generator performs an electrical power generating action. The capacitor also supplies electric power which is stored in the capacitor to the motor-generator via a driver such as a power generation inverter, or supplies the electric power to an electric power load such as an electric motor for driving the working machine.
The capacitor degrades when used over a long period, with repetitive operations of charge and discharge, or by heat generation, etc. Especially, in construction equipment which is operated in a harsh environment, a capacitor mounted in the equipment is prone to quickly degrade. When the degradation of the capacitor has progressed, the hybrid construction equipment lowers its work capability due to the lowering of electric power to be supplied to the electric motor. For this reason, degradation state of the capacitor should be determined in advance, and if it is determined that the degradation state has progressed to the limit, a necessary maintenance such as exchange of the capacitor is required.
As techniques for determining the degradation state of a capacitor, there are the following techniques.
(Conventional Art 1)
As methods for determining the degradation state of a capacitor which are being executed currently, there is a method in which a capacitance of a capacitor is measured using a high-output discharge device which is prepared for servicemen, and it is determined whether the measured capacitance becomes equal to or smaller than a prescribed capacitance. If the measured capacitance value becomes the prescribed capacitance or smaller, maintenance for exchanging capacitors is performed. In this method, firstly, an operation is conducted so that a capacitor mounted on the hybrid construction equipment is dismounted and the capacitor is carried to a place where a high-output discharge device is located to connect the capacitor to the high-output discharge device. Then, charge and discharge are repeated in the capacitor using the high-output discharge device and a voltage value and a current value are detected at that time. Further, capacitance of the capacitor is measured based on the detected voltage value and current value, and it is determined whether the measured capacitance becomes equal to or smaller than the prescribed capacitance.
(Conventional Art 2)
Patent document 1 discloses an invention in which a capacitor is supplied with an electric power from a buck-boost converter unit, a voltage value and a current value of the capacitor during the time are detected, an internal resistance value of the capacitor is calculated based on the detected voltage value and current value, and a degradation state of the capacitor is determined based on the calculated internal resistance value.
Patent document 1: Japanese patent application publication no. 2007-155586